1. Field of the Invention
The present invention relates to an electric power tool, particularly a chisel hammer, drill hammer or combination hammer, and including an external housing, a percussion mechanism arranged in the external housing, a motor for driving the percussion mechanism, a gear unit for connecting the driving motor with the percussion mechanism, and means for cooling the driving motor and the gear unit and including a fan element located in the external housing for generating a cooling air flow in the external housing, and a cooling air channel extending along a longitudinal extent of the percussion mechanism.
2. Description of the Prior Art
When operating electric power tools of the type mentioned above, the driving motor, percussion mechanism, gear units, and any existing electronics, as heat-generating components, generate heat that must be removed in order to prevent overheating of the electric power tool and of the heat-generating components. A flow of cooling air is generated in the external housing by means of a fan element. Fresh air is sucked in via intake openings in the external housing and is guided over the components of the electric power tool that generate heat during operation. Subsequently, the heated air is blown out again via blow-off openings in the external housing.
Heat develops at high temperature levels in the region of the percussion mechanism due to the percussion processes, the wall friction between the interacting percussion members of the percussion mechanism, and the transmission of heat from the pneumatic spring to the device during the compression stroke. Besides the high thermal stress on the percussion mechanism, the region of the electric power tool also serves to guide and hold the percussion mechanism. In order to maintain a low contact temperature in this region, the metal percussion mechanism housing is insulated, for example, by an additional housing shell made of plastic.
The known solution is disadvantageous in that the additional housing shell is not always sufficiently robust for operation on a construction site and often has special design requirements. There are also additional production costs.
DE 196 26 254 A1 discloses an electric power tool having an external housing within which are provided a driving motor and an percussion mechanism for driving a working tool in a rotating and/or percussive manner, which working tool is arranged in a tool holder of the electric power tool. The percussion mechanism is connected with the driving motor via a gear unit. A flow of cooling air for cooling the heat-generating components of the electric power tool is generated by a fan element in the external housing which is driven directly by the driving motor, for example. The housing of the percussion mechanism is arranged at a distance in order to form a cooling air channel extending parallel to a longitudinal extension of the percussion mechanism. When operating the electric power tool, the flow of cooling air in the external housing streams around any existing electronics and around the driving motor and gear unit and is guided past the percussion mechanism through the cooling air channel to the tool holder and blown out through blow-off openings at the tool holder.
This known solution is disadvantageous in that the percussion mechanism is located at the end of the cooling chain and the cooling air has already been heated by the other heat-generating component parts of the electric power tool. When the temperature of the cooling air flow is already high after cooling the other heat-generating components, the percussion mechanism is hardly cooled down by the cooling air which has been guided through the cooling air channel and which is already heated; in extreme cases, the percussion mechanism is even heated. The service life of the percussion mechanism is reduced because critical lubricating space and sealing space is thermally overloaded.
DE 198 39 963 A1 discloses another generic electric power tool which sucks in surrounding air by means of a fan element through two separate cooling air channels which are formed in the external housing and from which the air is blown out mixed together through a blow-off opening. The first cooling air flow streams around the electronics and the driving motor. The second cooling air flow streams around the percussion mechanism and the gear unit. Since the second cooling air flow is not preheated by other heat-generating components of the electric power tool, overheating of the percussion mechanism is prevented to a great extent.
Although the problem of cooling the heat-generating components of the electric power tool is solved in an advantageous manner in this electric power tool, there is still a need to improve the cooling thereof. Since two separate cooling air flows are generated by a fan element, the fan element has a high energy requirement or at least two fan elements are needed. Further, this solution for cooling the electric power tool requires dividing walls in the external housing of the electric power tool in order to prevent a short circuit of the air between the cooling air flows.